Method of making pigmented paper



Patented June 25, 1935 I i METHOD OF MAKING PIGMENTEDPAPER Alwin C. Eide and John Henry Calbeck, Columbus, Ohio, assignors to American Zinc, Lead &. Smelting Company, St. Louis, Mo., a corporation of Maine No Drawing. Application July 31, 1934, Serial No. 737,856

25 Claims. (CI. 92-21) This invention relates to pigmented papers and sulfide pigment with good opacity without calmore particularly to the method of making the cining. This made it impractical to use zinc sulsame, and has for its object to produce paper of fide in the undried or sludge form. The steps this kind in which the pigment is thoroughly and involved in drying and calcining zinc sulfide inefficiently incorporated with the fibers of the troduce additional costs and make a pigment 5 paper at a reduced cost, and with improved color that is less easily retained by the paper pulp. and opacity incident to the use of the pigment. A zinc sulfide precipitated slowly develops a It has heretofore been the practice to incorcrystalline rather than a colloidal structure, and porate zinc sulfide pigments in paper for the therefore develops whitening strength. The

purpose of improving opacity and the weight of method of this invention involves incorporating 10 the paper, the zinc sulfide in recent years used a wet crude zinc sulfide as precipitated, and not for this purpose being of the calcined type. mufiied, that has been so precipitated as to de- However, uncalcined or crude zinc sulfide pigvelop whitening strength before mufiling. One ments have been used primarily to give weight method of making a high opacity zinc sulfide to the paper, but because such uncalcined pigsuitable for carrying out this invention is dis- 5- ments do not possess high opacity, they have closed in the U. S. application of John H. Calbeen displaced by cheaper materials of equivabeck, Serial No. 688,413, filed September 6, 1933, lent opacity, such as blanc fixe. resulting in a pigment of crystalline form of uni- In the present practice in the paper making form size, and having a color strength, whiteness art, white pigments are incorporated in paper and brightness of unusual quality. Briefly 20 primarily to improve the color and opacity, and stated, the process set forth in said application it has been found that uncalcined zinc sulfides is as follows: as heretofore prepared cannot be used success- A zinc sulfate solution of about 28 Bais prefully for this purpose. Moreover, crude (uncalpared and brought to boiling. A chemically cined) zinc sulfides as heretofore prepared are equivalent volume of a thiosulfate (sodium or 25 not only inferior in color and opacity to the calammonium thiosulfate) is prepared of about 38 cined zinc sulfides but they have a harsh texture B. and purified of sulflte and sulfide. This soluwhich makes them diflicult to employ. tion is brought to boiling and a predetermined The amount of white pigment required to proamount (300 mg. per liter) of sodium sulfide is 30 duce a desired opacity in the finished paper deadded to provide a control of particle size. The 30 pends largely upon two factors; 1. Retention two boiling solutions are rapidly mixed and vigorof the pigment by the paper fibers, and 2. The ously agitated, and sodium carbonate or other natural opacity or obscuring power of the pigalkali base (or ammonia) is slowly added to mainment. In order that the cost of pigmentation tain a constant pH in the mixture. For the pur- 5 may not be excessive, all or nearly all of the pigpose of controlling the pH of said mixture, there ment added to the paper pulp should be retained is immersed therein electrodes of pure antimony by the finished paper and not washed out with and pure zinc connected by suitable wires to a the waste waters. This retention largely depotentiometer, and the base is added to the prepends upon the extent to which the pigment is cipitation mixture at such a rate as to maintain absorbed by the paper fiber, that is, the extent the E. M. F. across the electrodes of about 700 my. 40 to which the paper fiber and the pigment par- The boiling, agitation and addition of the base is ticles cling together by mutual attraction. This continued until the reaction is complete. When absorptive property of zinc sulfide is largely re-- complete, the mixture consists of a suspension of duced by calcining because of the physical a basic hydrated zinc sulfide with a combined changes taking place on the surface of the parzinc oxide content of from 3% to 5% in a satu- 45 ticles and because of the sintering together of rated solution of sodium sulfate (or other alkali many small particles to form aggregates, thereor ammonium sulfate). The precipitateisfiltered by reducing the active surface of the pigment. and washed free of the sulfate solution.

Opacity or obscuring power of the pigment is According to the present invention the wet (that largely a function of the refractive index of the is, undried) washed filtered cake or pulp is added 50 particle and the particle-size. 'Because of, the in any required quantity to paper pulp in the exceptionally high refractive index of zinc sulpulp machine for incorporation in the paper. fide it has been used extensively in the manu- Pigmentation by this method results in a neglifacture of pigments for paints. But heretofore gible loss of pigment in the waste water because it has not been found possible to prepare zinc of the high absorptive property and perfect dis- 55 persion of the undried precipitated pigment. Paper so produced has a wide range of opacities with a marked improvement in color, brightness and resistance to degradation.

The zinc sulfide produced by the above indicated method does not require mufiling, since the desired particle size can be obtained at the time of precipitation over a range from very fine to coarse, but in order to obtain exceptionally high opacities it is sometimes desirable to dehydrate the zinc sulfide in the sense of removing all or part of the water of crystallization or absorbed H2O without actually drying or calcining. This can be done by heating the wet pulp under pressure. It has been found that this dehydration can be accomplished by heating to 200 C. to 35c C. under the corresponding steam pressure.

Instead of precipitating the zinc sulfide and then incorporating the wet washed filtered cake or pulp in the paper pulp, as set forth above, the process may be modified by mixing the wet sulfide precipitate in large quantities with a small quantity of paper pulp and then this paper pulp is in turn mixed with the paper pulp in a pulp machine. Furthermore, the zinc sulfate and alkali thiosulfate solutions may be added to the paper pulp as such, and the mixture boiled and maintained at a substantially constant pH by the corntinuous addition of a base until the reaction is complete; or, oneof these solutions, either zinc sulfate or basic thiosulfate solution, may be added to the paper pulp and remain in contact therewith until a certain amount thereof is absorbed by the pulp, and then the other solution added and the mixture boiled while maintaining a substantially constant pH by the continuous addition of a base until reaction is complete. In this case a substantial amount of the zinc sulfide will be precipitated directly in the pulp and produce a betted bond between it and the precipitated zinc sulfide.

Whatever may be the method employed for incorporating the zinc sulfide in the paper pulp while in a wet or undried condition, there results a superior bond between the precipitated zinc sulfide and the fibers of the pulp, and hence a very material saving in the zinc sulfide itself, since this intimate bond between the zinc sulfide and the pulpprevents the loss of the sulfide through the medium of the waste water.

While, for the purpose of describing the invention, certain examples of the method employed have been set forth in specific detail herein, it will be understood that various other modifications thereof may be practiced Without departing from the spirit of the invention, and that such examples are not designed to define the limits of the invention, reference being had to the a,- pended claims for this purpose.

Having thus described the invention, what is claimed is:

a 1. In a process of making pigmented paper, the step of incorporating undried zinc sulfide in the paper pulp.

2. In a process of making pigmented paper, the step of incorporating undried zinc sulfide having a combined zinc oxide content of from two of five percent in the paper pulp.

3. In a process of making pigmented paper, the step of incorporating undried zinc sulfide the paper pulp by adding the to the under agitation.

i. In a process of making pigmented paper, the step of incorporating undried nnc sulfide hav ing a combined zinc oxide content of from twc to five percent in the paper pulp by adding the same to the pulp under agitation.

5. In a process of making pigmented paper,

the step of incorporating undried zinc sulfide in the paper pulp by precipitating the sulfide in the presence of the pulp.

6. In a process of making pigmented paper, the step of incorporating undried zinc sulfide having a combined zinc oxide content of from two to five percent in the paper pulp by precipitating the same in the presence of the pulp.

7. In a process of making pigmented paper, the step of incorporating undried zinc sulfide in the paper pulp by incorporating the same in excess in a small amount of pulp and then adding this pulp-zinc-sulfide composition to the main body of the pulp.

8. In a process of making pigmented paper, the step of incorporating undried zinc sulfide having a combined zinc oxide content of from two to five percent in the paper pulp by incorporating the same in excess in a small amount of pulp and then adding this pulp-zinc-sulfide composition to the main body of the pulp.

9. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide in the paper pulp.

10. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide having a combined zinc oxide content of from two to five percent in the paper pulp.

11. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide in the paper pulp by adding the same to the pulp under agitation.

12. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide having a combined zinc oxide content of from two to five percent in the paper pulp by adding the same to the pulp under agitation.

13. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide in the paper pulp by precipitating the sulfide in the presence of the pulp.

14. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide having a combined zinc oxide content of from two to five percent in the paper pulp by precipitating the same in the presence of the pulp.

15. In a process of making pigmented paper, the step of incorporating undried hydrated zinc sulfide in the paper pulp by incorporating the same in excess in a small amount of pulp and then add= ing this pulp-zinc-sulfide composition to the main body of the pulp.

16. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide having a combined zinc oxide content of from two to five percent in the paper pulp by incorporating the same in excess in a mall amount of pulp and then adding this pulpfine-sulfide composition to the main body of the pulp.

it. In a process of making pigmented paper, the step of incorporating undried basic zinc sul fide in the paper pulp by simultaneously adding zinc sulfate solution and an alkali thiosulfat/e solution to the pulp.

18. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide having a combined zinc oxide con tent of train two to five percent in the paper pulp by simultaneously adding zinc sulfate solution and an alkali thiosulfate solution to the pulp.

19. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide in the paper pulp by preparing solutions of zinc sulfate, and an alkali thiosulfate and mixing one of these solutions with the pulp and then adding the other solution to the mixture.

20. In a process of making pigmented paper, the step of incorporating undried basic hydrated zinc sulfide having a combined zinc oxide content of from two to five percent in the paper pulp by preparing solutions of zinc sulfate, and an alkali thiosulfate and mixing one of these solutions with the pulp and then adding the other solution to the mixture.

21. A method of making pigmented paper including the precipitation of a basic hydrated zinc sulfide by mixing chemically equivalent quantities of boiling solutions of zinc sulfate and an alkali thiosulfate, boiling and adding a base at a rate to maintain a constant pH in the mix and when the reaction is complete adding .the mixture to the paper pulp to incorporate the zinc sulfide therein.

22. A method of making pigmented paper including the precipitation of a zinc sulfide by mixing chemically equivalent qualities of boiling solutions of zinc sulfate and an alkali thiosulfate, boiling and adding a base at a rate to maintain a constant pH in the mix, and when the reaction is complete, washing the pigment free of soluble salts and adding it as a wet pulp to the paper pulp to incorporate the zinc sulfide therein.

23. A method of making pigmented paper including the precipitation of zinc sulfide by mixing boiling solutions of zinc sulfate and an alkali thiosulfate, boiling and adding a base at a rate to maintain a constant pH in the mix until the reaction is complete, washing the pigment free of soluble salts and treating the wet pulp with steam under pressures sufficient to maintain a temperature above 200 C. until a desired degree of dehydration of the pigment is accomplished, and then adding the treated'pulp to the paper pulp to incorporate the zinc sulfide therein.

24. A method of adding zinc sulfide pigment to paper which includes the prepicitation of the zinc sulfide on a small portion of paper pulp and adding the required amount of this master batch to a larger quantity of paper pulp to incorporate the zinc sulfide therein.

25. A method of precipitating a zinc sulfide pigment in the presence of paper pulp which comprises adding a mixture of zinc sulfate and an alkali thiosulfate to a paper pulp, boiling the mixture and maintaining a substantially constant pH by the continuous addition of a base until the reaction is complete.

ALWIN' C. EIDE. JOHN HENRY CALBECK. 

